Surveying the Challenges to Improve Linear Accelerator-based Radiation Therapy in Africa: a Unique Collaborative Platform of All 28 African Countries Offering Such Treatment

Radiation therapy is a critical component for curative and palliative treatment of cancer and is used in more than half of all patients with cancer. Yet there is a global shortage of access to this treatment, especially in Sub-Saharan Africa, where there is a shortage of technical staff as well as equipment. Linear accelerators (LINACs) offer state-of-the-art treatment, but this technology is expensive to acquire, operate and service, especially for low- and middle-income countries (LMICs), and often their harsh environment negatively affects the performance of LINACs, causing downtime. A global initiative was launched in 2016 to address the technology and system barriers to providing radiation therapy in LMICs through the development of a novel LINAC-based radiation therapy system designed for their challenging environments. As the LINAC prototype design phase progressed, it was recognised that additional information was needed from LMICs on the performance of LINAC components, on variables that may influence machine performance and their association, if any, with equipment downtime. Thus, a survey was developed to collect these data from all countries in Africa that have LINAC-based radiation therapy facilities. In order to understand the extent to which these performance factors are the same or different in high-income countries, facilities in Canada, Switzerland, the UK and the USA were invited to participate in the survey, as was Jordan, a middle-income country. Throughout this process, LMIC representatives have provided input on technology challenges in their respective countries. This report presents the method used to conduct this multilevel study of the macro- and microenvironments, the organisation of departments, the technology, the training and the service models that will provide input into the design of a LINAC prototype for a LINAC-based radiation therapy system that will improve access to radiation therapy and thus improve cancer treatment outcomes. It is important to note that new technology should be introduced in a contextual manner so as not to disrupt existing health systems inadvertently, especially with regards to existing staffing, infrastructure and socioeconomic issues. A detailed analysis of data is underway and will be presented in a follow-up report. Selected preliminary results of the study are the observation that LINAC-based facilities in LMICs experience downtime associated with failures in multileaf collimators and vacuum pumps, as well as power instability. Also, that there is a strong association of gross national product per capita with the number of LINACs per population.

Mobilising Expertise and Resources to Close the Radiotherapy Gap in Cancer Care

Closing the gap in cancer care within low- and middle-income countries and in indigenous and geographically isolated populations in high-income countries requires investment and innovation. This is particularly true for radiotherapy, for which the global disparity is one of the largest in healthcare today. New models and paradigms and non-traditional collaborations have been proposed to improve global equity in cancer control. We describe recent initiatives from within the radiation oncology community to increase access to treatment, build the low- and middle-income countries' radiation oncology workforce, mobilise more professionals from within high-income countries and raise awareness of the global need for equitable cancer care.

Public health oncology: a framework for progress in low- and middle-income countries

BACKGROUND

The problems of cancer are increasing in low- and middle-income countries (LMCs), which now have significant majorities of the global case and mortality burdens. The professional oncology community is being increasingly called upon to define pragmatic and realistic approaches to these problems.

PATIENTS AND METHODS

Focusing on mortality and case burden outcomes defines public health oncology or population-affecting cancer medicine. We use this focus to consider practical approaches.

RESULTS

The greatest cancer burdens are in Asia. A public health oncology perspective mandates: first, addressing the major and social challenges of cancer medicine for populations: human rights, health systems, corruption, and our limited knowledge base for value-conscious interventions. Second, adoption of evolving concepts and models for sustainable development in LMCs. Third, clear and realistic statements of action and inaction affecting populations, grounded in our best cancer science, and attention to these. Finally, framing the goals and challenges for population-affecting cancer medicine requires a change in paradigm from historical top-down models of technology transfer, to one which is community-grounded and local-evidence based.

CONCLUSION

Public health oncology perspectives define clear focus for much needed research on country-specific practical approaches to cancer control.

Normal tissue protection for improving radiotherapy: Where are the Gaps?

Any tumor could be controlled by radiation therapy if sufficient dose were delivered to all tumor cells. Although technological advances in physical treatment delivery have been developed to allow more radiation dose conformity, normal tissues are invariably included in any radiation field within the tumor volume and also as part of the exit and entrance doses relevant for particle therapy. Mechanisms of normal tissue injury and related biomarkers are now being investigated, facilitating the discovery and development of a next generation of radiation protectors and mitigators. Bringing recent research advances stimulated by development of radiation countermeasures for mass casualties, to clinical cancer care requires understanding the impact of protectors and mitigators on tumor response. These may include treatments that modify cellular damage and death processes, inflammation, alteration of normal flora, wound healing, tissue regeneration and others, specifically to counter cancer site-specific adverse effects to improve outcome of radiation therapy. Such advances in knowledge of tissue and organ biology, mechanisms of injury, development of predictive biomarkers and mechanisms of radioprotection have re-energized the field of normal tissue protection and mitigation. Since various factors, including organ sensitivity to radiation, cellular turnover rate, and differences in mechanisms of injury manifestation and damage response vary among tissues, successful development of radioprotectors/mitigators/treatments may require multiple approaches to address cancer site specific needs. In this review, we discuss examples of important adverse effects of radiotherapy (acute and intermediate to late occurring, when it is delivered either alone or in conjunction with chemotherapy, and important limitations in the current approaches of using radioprotectors and/or mitigators for improving radiation therapy. Also, we are providing general concepts for drug development for improving radiation therapy.

Assessing rectal toxicity in a pilot study using intrarectal amifostine and concurrent radiation

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Background: There is evidence that daily intrarectal amifostine can protect rectal mucosa during prostate cancer treatment. Instruments more sensitive than the RTOG score may discriminate small but clinically important reductions in proctitis, however these tools need further evaluation. This study used both the RTOG GI toxicity score and expanded prostate cancer index composite (EPIC), a patient-administered quality of life instrument, to evaluate toxicity. Methods: In this pilot study, patients with localized prostate cancer were given daily amifostine (MedImmune, INC., Gaithersburg, MD) which was placed per rectum 30–45 min before 3D conformal radiation (66–76 Gy in 2 Gy fractions to a volume based on PSA, Gleason score and clinical stage). The first 18 patients enrolled received 1gram of amifostine and the next 12 patients were given 2 grams. Toxicity was assessed at baseline, 5, and 7 weeks during treatment and 3, 6, 12, 18, and 24 months after radiation and amifostine treatment. RTOG grading, an EPIC score and proctoscopic examination were done. The EPIC questionaire is a validated instrument that consists of 50 quality of life questions related to urinary, bowel, sexual and hormonal domains. Two subsets of the bowel domain were used: “bowel function” (BF) targets symptom severity and “bowel bother,” (BB) assesses quality of life subscales. Results: Previously reported results demonstrate a clear trend towards protection from rectal toxicity using 2 gm as compared to a 1 gm amifostine dose. Here, we report that the EPIC-BF and EPIC-BB scores are both highly correlated with the RTOG toxicity score with a pearsons coefficient of 0.98 and 0.97 respectively at a median follow up of 24 mos. There was no significant change in the RTOG GI toxicity score over the course of treatment for either amifostine dose group. There was a statistically significant decrease in EPIC-BF score at 7 weeks (p = 0.04) and the EPIC-BB score showed a trend toward improvement (p = 0.07) at the same time point. The EPIC scores at all other time points were not statistically different from baseline. Conclusions: The EPIC score may be a more sensitive measure to detect acute toxicity associated with prostate cancer treatment but needs further investigation in the acute setting.

No significant financial relationships to disclose.

Transcriptional responses to ionizing radiation reveal that p53R2 protects against radiation-induced mutagenesis in human lymphoblastoid cells

The p53 protein has been implicated in multiple cellular responses related to DNA damage. Alterations in any of these cellular responses could be related to increased genomic instability. Our previous study has shown that mutations in p53 lead to hypermutability to ionizing radiation. To investigate further how p53 is involved in regulating mutational processes, we used 8K cDNA microarrays to compare the patterns of gene expression among three closely related human cell lines with different p53 status including TK6 (wild-type p53), NH32 (p53-null), and WTK1 (mutant p53). Total RNA samples were collected at 1, 3, 6, 9, and 24 h after 10 Gy gamma-irradiation. Template-based clustering analysis of the gene expression over the time course showed that 464 genes are either up or downregulated by at least twofold following radiation treatment. In addition, cluster analyses of gene expression profiles among these three cell lines revealed distinct patterns. In TK6, 165 genes were upregulated, while 36 genes were downregulated. In contrast, in WTK1 75 genes were upregulated and 12 genes were downregulated. In NH32, only 54 genes were upregulated. Furthermore, we found several genes associated with DNA repair namely p53R2, DDB2, XPC, PCNA, BTG2, and MSH2 that were highly induced in TK6 compared to WTK1 and NH32. p53R2, which is regulated by the tumor suppressor p53, is a small subunit of ribonucleotide reductase. To determine whether it is involved in radiation-induced mutagenesis, p53R2 protein was inhibited by siRNA in TK6 cells and followed by 2 Gy radiation. The background mutation frequencies at the TK locus of siRNA-transfected TK6 cells were about three times higher than those seen in TK6 cells. The mutation frequencies of siRNA-transfected TK6 cells after 2 Gy radiation were significantly higher than the irradiated TK6 cells without p53R2 knock down. These results indicate that p53R2 was induced by p53 protein and is involved in protecting against radiation-induced mutagenesis.

Workshop on Partial Breast Irradiation: State of the Art and the Science, Bethesda, MD, December 8-10, 2002

Breast conserving surgery followed by radiation therapy has been accepted as an alternative to mastectomy in the management of patients with early-stage breast cancer. Over the past decade there has been increasing interest in a variety of radiation techniques designed to treat only the portion of the breast deemed to be at high risk for local recurrence (partial-breast irradiation [PBI]) and to shorten the duration of treatment (accelerated partial-breast irradiation [APBI]). To consider issues regarding the equivalency of the various radiation therapy approaches and to address future needs for research, quality assurance, and training, the National Cancer Institute, Division of Cancer Treatment and Diagnosis, Radiation Research Program, hosted a Workshop on PBI in December 2002. Although 5- to 7-year outcome data on patients treated with PBI and APBI are now becoming available, many issues remain unresolved, including clinical and pathologic selection criteria, radiation dose and fractionation and how they relate to the standard fractionation for whole breast irradiation, appropriate target volume, local control within the untreated ipsilateral breast tissue, and overall survival. This Workshop report defines the issues in relation to PBI and APBI, recommends parameters for consideration in clinical trials and for reporting of results, serves to enhance dialogue among the advocates of the various radiation techniques, and emphasizes the importance of education and training in regard to results of PBI and APBI as they become emerging clinical treatments.

The Harvard Joint Center for Radiation Therapy, 1968-1999: a unique concept and its relationship to the prevailing times in academic medicine

PURPOSE

Institutional structure, function, and philosophy reflect the organizational needs, and tend to mirror societal values of the times. For many years, the field of radiation oncology had among its major academic centers, an organization that served as a model for collaboration among health care institutions in an effort to serve the common good of its patients, hospitals, professional colleagues, and community. For over three decades, the Joint Center for Radiation Therapy (JCRT) was a leader in developing new organizational approaches for academic and clinical radiation oncology through the philosophy of collaboration in patient care, education, and research.

METHODS AND RESULTS

In tracing the development and changes in organizational philosophy and structure of the JCRT, one can see the impact on academic oncology and cancer care through the emergence of both radiation and medical oncology as independent subspecialties, the importance of the National Cancer Act of 1971 accompanied by the growth of the NIH research and training programs and, more recently, the effect of the changing attitudes and approaches of hospitals, academicians, practitioners, and policy makers to health care delivery, structures, and cooperation.

CONCLUSION

Lessons learned from the 31-year history of the JCRT may help provide organizational insight useful in guiding academic oncology and academic medical centers through periods of change.

Report of the 1997 SCAROP survey on resident training. Society of Chairmen of Academic Radiation Oncology Programs

RATIONALE AND OBJECTIVES

Members of the Society of Chairmen of Academic Radiation Oncology Programs (SCAROP) were surveyed in November 1997 to evaluate the current status of radiation oncology training in the United States and to help determine how it should be carried out in the coming decade.

MATERIALS AND METHODS

A detailed questionnaire was sent to all members of SCAROP; 68 of 82 questionnaires were returned, for a response rate of 83%.

RESULTS

The responses to the survey show a serious shortage of radiation oncologists in university settings, despite an apparent surplus in private practice. Although recent changes in health care have added additional clinical responsibilities for radiation oncologists in university practices, approximately 75% of the chairpersons answering the survey continue to give their faculty protected time for research. Even with additional research and teaching responsibilities, the average radiation oncologist in university practice saw 206 patients per year in 1997, a number similar to that reported by the Patterns of Care Study for radiation oncologists overall. Approximately two-thirds of respondents believe that academic chairs should strive to have all clinical faculty members participating in research. Nevertheless, most think that basic research is better performed by dedicated researchers with PhD degrees rather than radiologists with MD degrees. Most respondents believe that the training programs adequately prepare radiation oncologists for a career in academic medicine but do not provide good training in research. Eighty-four percent agreed that resident performance on the American Board of Radiology examination should be considered in the accreditation of residency programs in radiation oncology but should not be the major criterion.

CONCLUSION

There is a shortage of academic radiation oncologists in the United States despite the large number of radiation oncologists completing training. This probably is due to a variety of factors, including a relatively small pool of candidates for academic positions, increasing demands for performance from academic physicians (to see more patients, perform research, publish, write grants, and teach), and competition from the private sector for recruitment of these individuals.

Molecular biology in radiation oncology. Radiation oncology perspective of BRCA1 and BRCA2

The breast cancer susceptibility genes, BRCA1 and BRCA2, are used to illustrate the application of molecular biology to clinical radiation oncology. Identified by linkage analysis and cloned, the structure of the genes and the numerous mutations are determined by molecular biology techniques that examine the structure of the DNA and the proteins made by the normal and mutant alleles. Mutations in the non-transcribed portion of the gene will not be found in protein structure assays and may be important in gene function. In addition to potential deleterious mutations, normal polymorphisms of the gene will also be detected, therefore not all differences in gene sequence may represent important mutations, a finding that complicates genetic screening and counseling. The localization of the protein in the nucleus, the expression in relation to cell cycle and the association with RAD51 led to the discovery that the two BRCA genes may be involved in transcriptional regulation and DNA repair. The defect in DNA repair can increase radiosensitivity which might improve local control using breast-conserving treatment in a tumor which is homozygous for the loss of the gene (i.e., BRCA1 and BRCA2 are tumor suppressor genes). This is supported by the early reports of a high rate of local control with breast-conserving therapy. Nonetheless, this radiosensitivity theoretically may also lead to increased susceptibility to carcinogenic effects in surviving cells, a finding that might not be observed for decades. The susceptibility to radiation-induced DNA damage appears also to make the cells more sensitive to chemotherapy. Understanding the role of the normal BRCA genes in DNA repair might help define a novel mechanism for radiation sensitization by interfering with the normal gene function using a variety of molecular or biochemical therapies.

Constitutive activation of IkappaB kinase alpha and NF-kappaB in prostate cancer cells is inhibited by ibuprofen

Apoptotic pathways controlled by the Rel/NF-kappaB family of transcription factors may regulate the response of cells to DNA damage. Here, we have examined the NF-kappaB status of several prostate tumor cell lines. In the androgen-independent prostate tumor cells PC-3 and DU-145, the DNA-binding activity of NF-kappaB was constitutively activated and IkappaB-alpha levels were decreased. In contrast, the androgen-sensitive prostate tumor cell line LNCaP had low levels of NF-kappaB which were upregulated following exposure to cytokines or DNA damage. The activity of the IkappaB-alpha kinase, IKKalpha, which mediates NF-kappaB activation, was also measured. In PC-3 cells, IKKalpha activity was constitutively active, whereas LNCaP cells had minimal IKKalpha activity that was activated by cytokines. The anti-inflammatory agent ibuprofen inhibited the constitutive activation of NF-kappaB and IKKalpha in PC-3 and DU-145 cells, and blocked stimulated activation of NF-kappaB in LNCaP cells. However, ibuprofen did not directly inhibit IkappaB-alpha kinase. The results demonstrate that NF-kappaB is constitutively activated in the hormone-insensitive prostate tumor cell lines PC-3 and DU-145, but not in the hormone responsive LNCaP cell line. The constitutive activation of NF-kappaB in prostate tumor cells may increase expression of anti-apoptotic proteins, thereby decreasing the effectiveness of anti-tumor therapy and contributing to the development of the malignant phenotype.

Salicylic acid and aspirin inhibit the activity of RSK2 kinase and repress RSK2-dependent transcription of cyclic AMP response element binding protein- and NF-kappa B-responsive genes

Sodium salicylate (NaSal) and other nonsteroidal anti-inflammatory drugs (NSAIDs) coordinately inhibit the activity of NF-kappa B, activate heat shock transcription factor 1 and suppress cytokine gene expression in activated monocytes and macrophages. Because our preliminary studies indicated that these effects could be mimicked by inhibitors of signal transduction, we have studied the effects of NSAIDs on signaling molecules potentially downstream of LPS receptors in activated macrophages. Our findings indicate that ribosomal S6 kinase 2 (RSK2), a 90-kDa ribosomal S6 kinase with a critical role as an effector of the RAS-mitogen-activated protein kinase pathway and a regulator of immediate early gene transcription is a target for inhibition by the NSAIDs. NSAIDs inhibited the activity of purified RSK2 kinase in vitro and of RSK2 in mammalian cells and suppressed the phosphorylation of RSK2 substrates cAMP response element binding protein (CREB) and I-kappa B alpha in vivo. Additionally, NaSal inhibited the phosphorylation by RSK2 of CREB and I-kappa B alpha on residues crucial for their transcriptional activity in vivo and thus repressed CREB and NF-kappa B-dependent transcription. These experiments suggest that RSK2 is a target for NSAIDs in the inhibition of monocyte-specific gene expression and indicate the importance of RSK2 and related kinases in cell regulation, indicating a new area for anti-inflammatory drug discovery.

Developmental effects of intermittent prenatal exposure to 1,1,1-trichloroethane in the rat

The effects of daily three 1-h exposures to 7000 ppm 1,1,1-trichloroethane (TCE) on physical and behavioral development were examined in Sprague-Dawley rats exposed during the last week of gestation. A sham group was exposed to filtered air. Offspring of both groups were fostered to untreated dams. No significant group differences were detected in total maternal weight gain or food and water consumption, but differences were observed in initial litter characteristics, including a longer gestation period in the TCE group, a smaller number of litters delivered in the TCE group, and fewer live pups per litter in the TCE group. At birth, the total litter weight was less in the TCE group, but there was no significant difference in average pup weight. Pups prenatally exposed to TCE did not differ from shams in day of eye opening, pinnae detachment, or incisor eruption. The TCE group weighed less the first 2 weeks of life, was impaired in its ability to perform the inverted screen, negative geotaxis, and vertical screen tests, and had less forelimb grip strength. Locomotor activity was reduced in the TCE group, and the ratio of brain to body weight was reduced in TCE-exposed offspring. These data provide evidence for neurobehavioral teratogenicity of intermittent prenatal exposure to high concentrations of TCE in rats.

Phase I trial of the hypoxic cell cytotoxin tirapazamine with concurrent radiation therapy in the treatment of refractory solid tumors

PURPOSE

Patients with refractory solid tumors were treated with the combination of fractionated radiation therapy and multiple-dose intravenous tirapazamine to determine the toxicities and maximum tolerated dose of tirapazamine when given concurrently with radiation therapy.

METHODS

Patients received radiation therapy in accordance with standard treatment practice in relation to fraction size and number of fractions for their particular cancer. In all cases, the course of radiation therapy exceeded the time of tirapazamine administration. Initially, tirapazamine was administered 5 days per week for 2 weeks for a total of 10 doses. After the first 8 patients, the schedule was changed to 3 times per week (Monday, Wednesday, Friday) for 4 weeks for a total of 12 doses. Between 3 and 6 patients were treated at each dose level.

RESULTS

A total of 43 patients were treated in the study between 1991 and 1995. All patients were 18 years old or older, had a Karnofsky performance status of > or = 60% and had adequate hematologic, hepatic, and renal function. Dose escalation began at 9 mg/m(2)/dose and was increased using a modified Fibonacci schema. The maximum tolerated dose was not reached and dose escalation was stopped at 260 mg/m(2) because of other data that became available suggesting 330 mg/m(2) was associated with dose-limiting toxicity (1, 2).

CONCLUSION

Tirapazamine in doses of up to 260 mg/m(2) times 12 doses can be given safely with fractionated radiation therapy. This dose appears to result in adequate plasma exposure (2) for radiation sensitization, and this schedule is being tested in a Phase II trial by the Radiation Therapy Oncology Group to determine if tirapazamine is a radiation enhancer in the clinic.

Pretreatment nomogram for prostate-specific antigen recurrence after radical prostatectomy or external-beam radiation therapy for clinically localized prostate cancer

PURPOSE

To present nomograms providing estimates of prostate-specific antigen (PSA) failure-free survival after radical prostatectomy (RP) or external-beam radiation therapy (RT) for men diagnosed during the PSA era with clinically localized disease.

PATIENTS AND METHODS

A Cox regression multivariable analysis was used to determine the prognostic significance of the pretreatment PSA level, 1992 American Joint Committee on Cancer (AJCC) clinical stage, and biopsy Gleason score in predicting the time to posttherapy PSA failure in 1,654 men with T1c,2 prostate cancer managed with either RP or RT.

RESULTS

Pretherapy PSA, AJCC clinical stage, and biopsy Gleason score were independent predictors (P < .0001) of time to posttherapy PSA failure in patients managed with either RP or RT. Two-year PSA failure rates derived from the Cox regression model and bootstrap estimates of the 95% confidence intervals are presented in the format of a nomogram stratified by the pretreatment PSA, AJCC clinical stage, biopsy Gleason score, and local treatment modality.

CONCLUSION

Men at high risk (> 50%) for early (< or = 2 years) PSA failure could be identified on the basis of the type of local therapy received and the clinical information obtained as part of the routine work-up for localized prostate cancer. Selection of these men for trials evaluating adjuvant systemic and improved local therapies may be justified.

A blueprint for linking academic oncology and the community

The processes by which academic medicine will train the next generation of physicians and develop new knowledge have brought to the forefront the relationship between academic medical centers and community hospitals and practitioners. Over the past thirteen years, the Harvard Medical School Joint Center for Radiation Therapy (JCRT) has developed an integrated radiation oncology program designed to serve simultaneously the needs of the community, teaching hospitals, medical schools, and faculty. The structure and function of this program are described here, as are the challenges posed by the highly competitive health care marketplace. We believe that long-term vision should guide short-term goals. The success of academic-community collaborative programs depends not only on the good will and vision of the participants but also on the medical administration, academic leadership, policy makers, and politicians who define the principles and rules by which cooperation within the health care industry occurs.

Real-time magnetic resonance image-guided interstitial brachytherapy in the treatment of select patients with clinically localized prostate cancer

PURPOSE

This study was performed to establish the dose-localization capability and acute toxicity of a real-time intraoperative magnetic resonance (MR) image-guided approach to prostate brachytherapy in select patients with clinically localized prostate cancer.

METHODS AND MATERIALS

Nine patients with 1997 American Joint Commission on Cancer (AJCC) clinical stage T1cNxM0 prostate cancer, prostate-specific antigen (PSA) < 10 ng/ml, biopsy Gleason score not exceeding 3 + 4, and endorectal coil MR stage T2 disease were enrolled into this study. The prescribed minimum peripheral dose was 160 Gy to the clinical target volume (CTV), which was the MR-defined peripheral zone (PZ) of the prostate gland. Using a real-time 0.5 Tesla intraoperative MR imaging unit, 5-mm image planes were obtained throughout the prostate gland. The PZ of the prostate gland, anterior rectal wall, and prostatic urethra were identified on the T2 weighted axial images by an MR radiologist. An optimized treatment plan for catheter insertion was generated intraoperatively. Each catheter containing the 125Iodine sources was placed under real-time MR guidance to ensure that its position in the coronal, sagittal, and axial planes was in agreement with the planned trajectory. Real-time dose- volume histogram analyses were used intraoperatively to optimize the dosimetry.

RESULTS

For the 9 study patients, 89-99% (median 94%) of the CTV received a minimum peripheral dose of 160 Gy and > or = 95% of the volume of the prostatic urethra and 42-89% (median 70%) of the volume of the anterior rectal wall received doses that were below the reported tolerance. All patients voided spontaneously within 3 h after discontinuation of the Foley catheter and no patient required more than a limited course (< or = 3 weeks) of oral alpha-1 blockers for postimplant urethritis.

CONCLUSIONS

Real-time MR-guided interstitial radiation therapy provided the ability to achieve the planned optimized dose-volume histogram profiles to the CTV and healthy juxtaposed structures intraoperatively, with minimal acute morbidity.

Interaction of tomudex with radiation in vitro and in vivo

The potential of the thymidylate synthase inhibitor, Tomudex to interact with ionizing radiation was assessed in vitro and in vivo in comparison with 5-fluorouracil. A concentration of 1 microM Tomudex decreased the shoulder of the radiation survival curves for normally oxygenated and hypoxic human HT-29 colon carcinoma cells and human SCC-25 head and neck squamous carcinoma cells, resulting in enhancement ratios of 10 and 2.8 for normally oxygenated and hypoxic HT-29 cells at 5 Gray, respectively, and enhancement ratios of 19.5 and 2.7 for normally oxygenated and hypoxic SCC-25 cell at 5 Gray, respectively. Two schedules of Tomudex administered to animals bearing the Lewis lung carcinoma resulted in additive tumor growth delay with the fractionated radiation therapy. In nude mice bearing the HT-29 colon carcinoma grown as a xenograft, administration of Tomudex daily for 5 days on a 1 or 2-week schedule resulted in increased tumor growth delay along with fractionated radiation therapy on the same schedules. However, administration of Tomudex intermittently on a 2-week schedule appeared to be more interactive with daily fractionated radiation therapy on the 2-week schedule. In each assay, the results obtained with Tomudex were equal to or exceeded those obtained with 5-fluorouracil. These findings indicate that clinical trial of Tomudex along with fractionated radiation therapy is warranted.

Molecular Biology to Radiation Oncology: A Model for Translational Research? Opportunities in basic and translational research. From a workshop sponsored by the National Cancer Institute, Radiation Research Program, January 26-28, 1997, Bethesda, Maryland

Many exciting discoveries are being made that are providing new insights into how molecules, cells and tissues respond to ionizing radiation. There remains a need, however, to translate these findings into more effective treatments for cancer patients, including those treated with radiation therapy. This complex task will require the collaboration of scientists studying molecular, cellular and tissue responses, and those performing clinical trials of emerging therapies. The Radiation Research Program of the National Cancer Institute sponsored a workshop entitled "Molecular Biology to Radiation Oncology: A Model for Translational Research?" to bring together basic scientists and clinicians to exchange ideas and fundamental concepts and to identify opportunities for future research and collaboration. Four broad topics were addressed: signal transduction and apoptosis, the cell cycle, repair of radiation damage, and the microenvironment. The development, selection and use of appropriate experimental models is crucial to finding and developing new therapies, and opportunities exist in this area as well. This paper and the accompanying paper by Coleman and Harris that provides the viewpoint of radiation oncologists (Radiat. Res. 150, 134-147, 1998) summarize the background concepts and opportunities for translational research identified by the workshop participants.

Combined antitumor effect of radiation and ibuprofen in human prostate carcinoma cells

Recent clinical observations indicate that ibuprofen may alleviate the radiation-induced dysuria that almost invariably occurs during radiation therapy for prostate cancer. Because the use of ibuprofen could consequently become common during radiation therapy for prostate cancer, we have been interested in the potential interactions between ibuprofen and ionizing radiation on prostate tumor cells. The effects of gamma-irradiation and/or ibuprofen on PC3 and DU-145 human prostate carcinoma cells were evaluated in vitro using three model systems. Clonogenic survival was determined by plating cells 24 h after treatment of nearly confluent monolayers. Analysis of cell growth, cell detachment, and apoptotic cell death was carried out over a period of up to 9 days after treatment of PC3 and DU-145 monolayers. The effect of ibuprofen and/or radiation was also probed by observing the inhibition of growth of established PC3 and DU-145 colonies that were treated on the 14th day of colony growth. Ibuprofen enhanced the radiation response of prostate cancer cells in all three in vitro models. Both the cytotoxic and radiosensitizing effects of ibuprofen seem to require concentrations that are higher than those reported to inhibit prostaglandin synthesis, suggesting that other molecular mechanisms may be responsible for ibuprofen cytotoxicity.

Of what use is molecular biology to the practicing radiation oncologist?

BACKGROUND AND PURPOSE

We are in a period of rapid advance in understanding the basic mechanisms behind the induction and progression of cancer. The relevance of this new knowledge to the daily clinical practice of radiation oncology may not necessarily be readily apparent. Familiarity with a few of the concepts of molecular biology and biochemistry are necessary to fully appreciate the clinical relevance of the new biology.

METHODS AND RESULTS

To illustrate how the new knowledge affects the practice of radiation oncology, examples of the use of molecular biology are presented for different clinical aspects of clinical oncology, i.e. screening and prevention, prognostic factors, predictive factors, treatment decision, novel therapy and follow-up. A number of the molecular biology techniques are illustrated.

CONCLUSIONS

The advances from molecular biology directly impact the role of radiation oncologists in the clinic. While major new therapies are still in development in the laboratory, these will likely have a very significant role in patient care and cancer prevention in the not-too-distant future. Given the central role of radiation oncologists in cancer management, a basic knowledge of molecular biology techniques and their application is essential so that we can be current with our colleagues and patients and as a specialty, participate actively in improving the outcome of patients with or at risk of developing cancer.

Calculated prostate carcinoma volume: The optimal predictor of 3-year prostate specific antigen (PSA) failure free survival after surgery or radiation therapy of patients with pretreatment PSA levels of 4-20 nanograms per milliliter

BACKGROUND

In this study, the authors evaluated whether a clinically relevant stratification of prostate specific antigen (PSA) failure free survival (bNED) after definitive local therapy could be made for patients with prostate carcinoma clinically classified as T1 or T2 and pretreatment PSA levels of 4-20 ng/mL.

METHODS

Multivariate Cox regression analysis and Kaplan-Meier analysis were performed for clinically localized prostate carcinoma patients who presented with PSA levels of 4-20 ng/mL. Three hundred forty-eight of the patients were managed definitively with conventional external beam radiation therapy (median dose, 67 gray), whereas 547 of the patients were managed definitively with a radical retropubic prostatectomy. The outcome tested was time to posttreatment PSA failure. The clinical predictors evaluated included the standard paradigm (PSA, biopsy Gleason score, and clinical stage); type of local therapy; and a newly defined factor, the calculated prostate cancer volume (cV[Ca]).

RESULTS

Time to posttreatment PSA failure was equivalent (P = 0.52) independent of the type of local therapy. The cV(Ca) (P < 0.0001), pretreatment PSA (P = 0.003), and clinical classification of T2c (P = 0.04) remained significant predictors of time to posttreatment PSA failure in multivariate analysis.

CONCLUSIONS

The staging system described herein, which is based on cV(Ca) and PSA, may optimize patient selection for definitive local therapy and entry onto randomized clinical trials examining the use of adjuvant hormonal or chemotherapy in patients with clinically localized disease who present with PSA levels of 4-20 ng/mL. Validation of this staging system by other investigators is currently underway.

Survival results from a phase I study of etanidazole (SR2508) and radiotherapy in patients with malignant glioma

PURPOSE

To report the survival results from a previous Phase I study of etanidazole (ETA) and radiotherapy in patients with glioblastoma multiforme (GBM n = 50) or anaplastic astrocytoma (AA n = 19) and examine survival according to age, Karnofsky performance status (KPS), and implant status.

PATIENTS AND METHODS

In a previous Phase I study, 70 previously untreated patients (median age 49) with malignant gliomas were accrued. One patient was excluded from analysis because pathology was unverifiable. All had KPS > or = 70. Prior to initiation of treatment, patients were stratified according to whether they were candidates for interstitial implantation. The implant patients (IMP n = 14) received accelerated fractionation radiotherapy (XRT) 2 Gy BID (6 hours apart) to 40 Gy in 2 weeks with ETA 2 gm/m2 x 6 doses, a 2 week break, and then interstitial implant for an additional 50 Gy (4-7 days) with a continuous infusion of ETA over 90-96 hours. There were 55 patients treated on two sequentially conducted non-implant arms. These patients started with accelerated fractionation XRT 2 Gy BID (6 hours apart) to 40 Gy in 2 weeks with ETA 2 gm/m2 x 4-5 doses/week. Non-IMP1 arm (n = 41) received a 2-week break before standard fractionated boost XRT of 2 Gy/day for 2 weeks to a total dose of 60 Gy with ETA. Non-IMP2 arm (n = 14) did not have the 2-week break. All patients had plasma pharmacokinetic monitoring of ETA. Subsequent follow-up study provided information regarding long-term survival status of this group of patients. The Phase I toxicity evaluation was conducted according to the RTOG toxicity scale and was found well tolerated in both groups. Overall actuarial survival was plotted for all patients, by histologic group, and by implant status. Subset analyses of GBM patients by age (< or = 49 or > 49 years), KPS (< or = 80 or > 80) and implant versus non-implant were also performed.

RESULTS

Median survival of GBM patients was 1.1 years and that of anaplastic astrocytoma patients was 3.1 years (p = 0.0001). In GBM patients, KPS > 80, implanted patients, and age < or = 49 were factors found not to be associated with a statistically improved survival.

CONCLUSION

The results of survival in this Phase I etanidazole study of patients with anaplastic astrocytoma are comparable to the results from other studies using bromodeoxyuridine, iododeoxyuridine, or procarbazine, lomustine (CCNU), and vincristine. The use of etanidazole with accelerated radiotherapy does not appear to improve survival in patients with glioblastoma multiforme compared to those treated with conventional therapies.

Pharmacokinetic monitoring and dose modification of etanidazole in the RTOG 85-27 phase III head and neck trial

PURPOSE

To prospectively evaluate the pharmacokinetic monitoring and drug dose adjustment of Etanidazole (Eta) in patients treated on the RTOG randomized trial for Stage III and IV head and neck cancer.

METHODS AND MATERIALS

From June, 1986 to October, 1991, 521 patients were randomized to conventional RT alone or RT plus Eta. The primary goal was to determine whether the addition of Eta to conventional radiation therapy improves local-regional control and tumor-free survival. Of the 264 patients who received Eta, 233 had their drug exposure calculated and the Eta dose and schedule adjusted accordingly to prevent the occurrence of serious peripheral neuropathy. Drug exposure was assessed using the area under the curve (AUC) for a single treatment that was calculated by the integral over time of the serum concentration of Eta. The total drug exposure (total-AUC) was estimated by multiplying the AUC by the number of drug administrations.

RESULTS

Eighteen percent of patients developed Grade I and 6% developed Grade II peripheral neuropathy. There was no Grade 3 or 4 peripheral neuropathy. There is a trend for an increased risk of neuropathy by single dose AUC. The minimal difference in incidence of neuropathy by single-dose AUC was due to the use of dose and schedule modification for patients with the higher values.

CONCLUSIONS

The pharmacokinetics investigated in this study confirm previous work that monitoring Eta levels, with dose adjustment, allows it to be used safely in the clinic. In a subset analysis there was a statistically significant improvement in local-regional control and survival rates for patients with N0 and N1 disease, that will require confirmation (14). However, the clinical efficacy of Eta in this trial proved to be of little overall benefit.

Equivalent 5-year bNED in select prostate cancer patients managed with surgery or radiation therapy despite exclusion of the seminal vesicles from the CTV

PURPOSE

Prostate Specific Antigen (PSA) failure free survival was determined for select prostate cancer patients managed definitively with external beam radiation therapy to the prostate only or radical retropubic prostatectomy.

METHODS AND MATERIALS

A logistic regression multivariable analysis evaluating the variables of PSA, biopsy Gleason score, and clinical stage was used to evaluate the endpoint of pathologic seminal vesicle invasion (SVI) in 749 consecutive prostate cancer patients managed with a radical retropubic prostatectomy. In a subgroup of 332 surgically and 197 radiation managed patients who did not have the clinical predictors of SVI, PSA failure free survival (bNED) was determined. Comparisons were made using the log rank test between surgically and radiation managed patients in this subgroup. In this subgroup, radiation managed patients were treated to a median dose of 66 Gy (66-70 Gy) to the prostate only.

RESULTS

The pretreatment PSA (> 10 ng/ml), biopsy Gleason score (> or = 7), and clinical stage (T2b, 2c, or 3) were found to be significant independent predictors (p < 0.001) of SVI. Only 2% of patients without any of these factors had SVI and 17% had extracapsular extension (15% microscopic; 2% macroscopic). In this subgroup the 5-year bNED rates were equivalent [84 vs. 89% (p = 0.67)] for surgically and radiation managed patients, respectively.

CONCLUSIONS

Conventional dose external beam radiation therapy directed at the prostate alone resulted in 5-year bNED rates equivalent to surgery on retrospective comparison in patients with clinical stage T1,2a, PSA < or = 10 ng/ml, and biopsy Gleason < or = 6 prostate cancer.

Stage IA-IIB Hodgkin's disease: management and outcome of extensive thoracic involvement

PURPOSE

To examine the presentation, management, and outcome of patients with extensive intrathoracic involvement in early-stage Hodgkin's disease.

PATIENTS AND METHODS

One hundred seventy-two patients with clinical Stage IA-IIB Hodgkin's disease and extensive intrathoracic involvement were studied. Extensive intrathoracic disease was defined as either large mediastinal adenopathy (LMA, defined as the width of the mass greater than one-third the maximum thoracic diameter, n = 154) or as extensive (> 10 cm) cephalocaudad intrathoracic disease that did not fulfill formal chest radiograph criteria for LMA (n = 18). Patients were divided into three groups based on staging and extent of treatment. Forty-seven patients were treated with radiation alone after a laparotomy (RT-lap), 47 patients received combined modality therapy after laparotomy (CMT-lap), and 78 patients were treated with combined modality therapy without staging laparotomy (CMT-no lap). MOPP was used in 82% of the CMT patients. Low-dose whole-cardiac RT was used in nearly 50% of patients treated either with RT or CMT.

RESULTS

The 10-year actuarial freedom from relapse rates were 54% with RT alone and 88% with CMT (p = 0.001); overall survival rates were 84 and 89%, respectively (p = NS). The median time to relapse was only 17 months. Over 80% of relapses occurred within the first 3 years. The most common site of relapse in all patients was the mediastinum. Relapses below the diaphragm were rare, even in CMT patients who did not receive abdominal radiation treatment. The principal acute morbidity was symptomatic pneumonitis, which occurred in 29% of patients receiving any part of their chemotherapy after RT, compared to 13% if all the chemotherapy was given before RT and 11% if RT alone was administered. There was a low late risk of myocardial infarction (3%) in the two groups with the longest follow up (RT-lap, CMT-lap), but a higher risk of second malignancy in the CMT-lap group (21%) compared with the RT-lap group (2%).

CONCLUSION

Extensive intrathoracic involvement is a distinctive presentation of early-stage HD that has a high relapse risk if treated with RT alone. The introduction of CMT has been associated with improvements in freedom from relapse. The low rate of peripheral relapse with CMT suggests that reductions in field size may be achievable. The use of low-dose whole-heart RT with modern techniques is not associated with a high risk of late cardiac complications and should be used in patients who present with extensive pericardial disease or cardiophrenic lymphadenopathy. The high rate of second malignancy in the CMT group with the longest follow-up suggests that careful long-term surveillance for such patients is warranted.

Apoptosis and clonogenic cell death in PC3 human prostate cancer cells after treatment with gamma radiation and suramin

Suramin is a novel cytostatic/cytotoxic agent that is currently undergoing clinical trials in the treatment of hormone- and chemo-refractory tumors. Its unusual mechanism of action and its activity against prostate cancer raise the possibility that it could be particularly suitable for combined-modality treatment of prostate cancer. PC3 human prostate cancer cells were used as an in vitro model to test the possible interaction between suramin and ionizing radiation. Treatment with gamma radiation resulted in detachment of PC3 cells from the monolayer, and the detached cells exhibited internucleosomal DNA fragmentation characteristic of apoptosis. Low concentration of suramin (50-100 micrograms/ml, 35-70 microM) increased spontaneous as well as radiation-enhanced apoptosis. However, suramin inhibited spontaneous and radiation-enhanced apoptosis at 300 micrograms/ml (210 microM), a concentration that is more commonly used in the clinic. At this concentration suramin inhibited DNA fragmentation induced by chemotherapeutic drugs as well. The effect of suramin on inhibition of DNA fragmentation was reversible if the suramin was removed 24 h after irradiation. Despite inhibition of radiation-induced apoptosis by 300 micrograms/ml suramin (from 5% to 2.9% at 48 h), clonogenic cell death was enhanced by the combination of suramin and radiation. The effects of radiation and suramin on clonogenic cell survival appeared to be additive by isobologram analysis at clinically relevant radiation doses. Continuous exposure to a lower concentration of suramin (100 micrograms/ml) during the clonogenic assay period was as effective in decreasing clonogenic survival as 48 h exposure to 300 micrograms/ml suramin in decreasing clonogenic survival. Our data indicate that, when used in combination with radiation, suramin may be effective at concentrations that are lower than those required for efficacy as a single agent.

Equivalent biochemical failure-free survival after external beam radiation therapy or radical prostatectomy in patients with a pretreatment prostate specific antigen of > 4-20 ng/ml

PURPOSE

Biochemical failure-free survival stratified by the pretreatment prostate-specific antigen (PSA) and biopsy Gleason score (bGl) is determined for prostate cancer patients managed definitively with external beam radiation therapy or radical retropubic prostatectomy.

METHODS AND MATERIALS

A Cox regression multivariable analysis evaluating the variables of PSA, bGl, and clinical stage was used to evaluate the end point of time to PSA failure in 867 and 757 consecutive prostate cancer patients managed definitively with external beam radiation therapy or radical retropubic prostatectomy, respectively. PSA failure-free survival was determined using Kaplan-Meier analysis. Comparisons were made using the log rank test.

RESULTS

The pretreatment PSA, bGl, and clinical stage (T3,4 vs. T1,T2) were found to be independent predictors of time to post-treatment PSA failure for both surgically and radiation managed patients using Cox regression multivariable analysis. Patients with a pretreatment PSA of > 4 ng/ml and < or = 20 ng/ml could be classified into risk groups for time to post-therapy PSA failure: low = PSA > 4-10 ng/ml and bGl < or = 4; intermediate = PSA > 4-10 and bGl 5-7; or PSA > 10-20 ng/ml and bGl < or = 7; high = PSA > 4-20 ng/ml and bGl > or = 8. Two-year PSA failure-free survival for surgically managed and radiation-managed patients, respectively, were 98% vs. 92% (p = 0.45), 77% vs. 81% (p = 0.86), and 51% vs. 53% (p = 0.48) for patients at low, intermediate, and high risk for post-therapy PSA failure.

CONCLUSIONS

There was no statistical difference in the 2-year PSA failure-free survival for potentially curable patients managed definitively with surgery or radiation therapy when a retrospective comparison stratifying for the pretreatment PSA and bGl was performed.

Results of a phase II trial of external beam radiation with etanidazole (SR 2508) for the treatment of locally advanced prostate cancer (RTOG Protocol 90-20)

PURPOSE

RTOG Protocol 90-20 was designed to evaluate the effect of the hypoxic cell sensitizer Etanidazole (SR-2508) on locally advanced adenocarcinoma of the prostate treated with concurrent external beam irradiation.

METHODS AND MATERIALS

Patients with biopsy-proven adenocarcinoma of the prostate with locally advanced T2b, T3, and T4 tumors were eligible for this study. No patients with disease beyond the pelvis were eligible. Serum prostate specific antigen (PSA) was mandatory. All patients received definitive external beam irradiation using standard four-field whole pelvis treatment to 45-50 Gy, followed by a cone down with a minimum total dose to the prostate of 66 Gy at 1.8-2.0 Gy/fraction over 6.5-7.5 weeks. Etanidazole was delivered 1.8 g/m2 given 3 times a week to a total of 34.2 g/m2 or 19 doses.

RESULTS

Thirty-nine patients were entered onto the study. Three patients refused treatment; therefore, 36 patients were eligible for further evaluation. Median follow-up was 36.9 months from treatment end. All patients had elevated initial PSA levels, and 18 patients had PSAs of > 20 ng/ml. Tumor classification was T2, 12 patients (33.3%); T3, 22 patients (61.1%); and T4, 2 patients (5.6%). Complete clinical response, defined as PSA < 4 ng/ml and complete clinical disappearance, was attained in 17.9% of (5/28 pts) with information at 90 days and 56% of patients by 12 months following treatment. Relapse-free survival was 13% at 3 years with PSA < 4 ng/ml. There were no Grade 4 or 5 toxicities, either acute (during treatment) or in follow-up.

CONCLUSIONS

Results of this trial regarding PSA response and clinical disappearance of disease are similar to historical controls and do not warrant further investigation of etanidazole as was done in this trial. Drug toxicity that, in the past, has been unacceptably high with other hypoxic cell sensitizers does not appear to be a significant problem with this drug.

Effect of BSO and etanidazole on neurofilament degradation in neonatal rat spinal cord cultures

Peripheral neuropathy is the major dose-limiting toxicity of the hypoxic cell sensitiser, etanidazole. Previous work from this laboratory using culture neuronal cell lines suggested that nitroimidazole-induced degradation of neurofilament proteins might be the critical biological event mediating this neurotoxicity. The purpose of the present study was to develop the neurofilament degradation assay in an organotypic spinal cord culture system with the goal of developing strategies for optimising sensitiser efficacy as well as ameliorating nitroimidazole-induced neurotoxicity. Spinal cord cultures were treated with etanidazole and neurofilament protein degradation was analysed by immunoblot analysis. Spinal cord cultures exposed to etanidazole exhibited a dose-dependent loss of parent neurofilament proteins, with concomitant appearance of low molecular weight degradation products. The potential neurotoxic effect of L, S-buthionine sulphoximine (BSO), a compound that enhances the radiosensitising effectiveness of 2-nitroimidazoles, was also screened in this assay system. BSO alone, at concentrations up to 100 microM, did not promote neurofilament degradation. BSO (20 microM) enhanced the effect of etanidazole on neurofilament degradation by a dose-modifying factor of 1.6 +/- 0.5. Since 20 microM BSO is expected to enhance etanidazole radiosensitisation of hypoxic cells by a larger factor, this suggests that a therapeutic gain could be achieved using BSO in combination with etanidazole in radiation therapy.

Vascular endothelial growth factor: environmental controls and effects in angiogenesis

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Second malignancies after treatment for laparotomy staged IA-IIIB Hodgkin's disease: long-term analysis of risk factors and outcome

The survival of patients with Hodgkin's disease has dramatically improved over the past 30 years because of advances in treatment. However, concern for the risk of long-term complications has resulted in a number of trials to evaluate reduction of therapy. The consequences of these trials on recurrence, development of long-term complications, and survival remain unknown. One major consequence of successful treatment of Hodgkin's disease is the development of second malignant neoplasms. We sought to determine the factors most important for development of second tumors in pathologically staged and treated Hodgkin's disease patients followed for long intervals to provide background information for future clinical trials and guidelines for routine patient follow-up. Between April 1969 and December 1988, 794 patients with laparotomy staged (PS) IA-IIIB Hodgkin's disease were treated with radiation therapy (RT) alone or combined radiation therapy and chemotherapy (CT). There were 8,500 person-years of follow-up (average of 10.7 person-years per patient). Age and gender-specific incidence rates were multiplied by corresponding person-years of observation to obtain expected numbers of events. Observed to expected results were calculated by type of treatment, age at treatment, sex, and time after Hodgkin's disease. Absolute (excess) risk was expressed as number of excess cases per 10,000 person-years. Seventy-two patients have developed a second malignant neoplasm. Eight patients developed acute leukemia, 10 had non-Hodgkin's lymphoma (NHL), and 53 patients developed solid tumors at a median time of 5 years, 7.25 years, and 12.2 years, respectively, after Hodgkin's disease. One patient developed multiple myeloma 16.5 years after Hodgkin's disease. The relative risk (RR) of developing a second malignancy was 5.6. The absolute excess risk per 10,000 person-years (AR) of developing a second malignancy was 69.6 (7.0% excess risk per person per decade of follow-up). The highest RR occurred for the development of leukemia (RR = 66.2), however because of the low expected risk, the AR was only 9.3. The RR of solid tumors after Hodgkin's disease was lower (4.7); however, the AR was greater (49) than for acute leukemia. Among the solid tumors, breast, gastrointestinal, lung, and soft tissue cancers had the highest absolute excess risks. The risk for developing breast cancer after Hodgkin's disease was greatest in women who were under the age of 25 at treatment. The most significant risk factor for the development of both leukemia and solid tumors was the combined use of radiation therapy and chemotherapy. The RR following RT alone was 4.1 (AR = 51.1); for RT + CT (initially or at relapse) the RR was 9.75 (P < 0.05, nonoverlapping confidence limits, AR = 123.9). Survival following development of a second malignancy was poor in patients with leukemia, gastrointestinal tumors, lung cancer, and sarcoma. Survival from other malignancies including NHL and breast cancer was more encouraging. Second malignant neoplasms are a major cause of late morbidity and mortality following treatment for Hodgkin's disease. The most significant risk factor for the development of second tumors is the extent of treatment for Hodgkin's disease. Recommendations are presented for both prevention and early detection of these tumors.

Biologic basis for radiation oncology

Improved understanding of the underlying biologic mechanisms that pertain to radiation oncology is providing an explanation for the cellular and tissue responses to ionizing radiation and is leading to the potential for novel therapeutic strategies. Among the areas of intensive investigation are: DNA recombination and repair, signal transduction, gene regulation, apoptosis, the cellular stress response, and the effect of the tumor microenvironment. These new biologic concepts, coupled with the superior technical capabilities now available for treatment delivery, are paving the way for new clinical approaches to improving both the quality and quantity of life for the cancer patient.